Hazardous materials, such as, for example, explosive materials, flammable materials, bio-hazardous materials, other types of materials that have a flash point, detonation or volatile ignition temperature that makes them hazardous, and in some cases, particularly chosen and developed for their hazardous properties, in for example, munitions applications, and the like, require safe storage, handling and disposal. Such materials are frequently stored and/or utilized in closed vessels. The closed vessels create challenges for the safe removal of the hazardous material, such as, for example, removing explosive material from munitions, and safe handling, such as, for transportation of munitions prior to desired deployment. The closed vessels also create challenges when the temperature of the closed vessel rises beyond the safe operating and handling temperature of the vessel.
Conventional pressure relief valves typically vent the contents of a closed vessel when the pressure in the vessel reaches a critical condition. However, conventional pressure relief valves do not provide a warning as to when a vessel is in a critical and an unsafe state.
Moreover, conventional pressure relief mechanisms may reduce the structural integrity of the closed vessel overall reducing the closed vessel capability to perform to its fullest potential under normal operating conditions.
In general, closed vessels have normal handling and operating temperatures between 60° F. to 160° F. In case of a fire, or other cause of extreme heat, the temperature of the closed vessel rises beyond a safe temperature of, for example, 160° F., the material contained inside the closed vessel expands and creates an increased internal pressure (hoop pressure). At a certain point, as the internal pressure increases, the closed vessel ruptures and creates a high order explosion. If this hoop pressure were to be relieved, the high order explosion can be reduced to a low order reaction. A low order reaction still has a flame and fire associated with it, but it does not explode. By eliminating the high order explosion, the hazardous material can be safely dealt with.
Safety is another important design aspect of transport and storage of volatile materials, as well as munitions, including, for example, artillery shells, bomblets, rockets, mortars, missiles, hand grenades and the like. For example, the propellants and explosives contained within munitions degrade over time, and thus their reliability decreases to an unacceptable level, resulting in munitions having a limited “shelf life”. When the shelf life of a given munition is reached, it is withdrawn from stock and replaced with a new munition. This results in a problem in that these withdrawn, but still “live” munitions with dangerous high energy explosives (“energetics”) and other hazardous materials, such as lead, must be “demilitarized,” i.e. rendered to a state where they are no longer capable of being used as a munition or otherwise causing a safety threat. In order to accomplish this, the energetics must be removed from the munition and disposed of safely. Demilitarization procedures frequently involve the intentional burning of the munition.
Consequently, munitions need to be rendered “safe” instead of going high order when exposed to high temperatures, either from, for example, an intentional or accidental fire. Typically, however, munitions are not provided with a “safe” mode for exposure to high temperatures. As a result, the risk of a high order detonation is significant.
Heat exposure may be a rapid exposure to high temperatures (a fast cook off condition), or a slow, sustained exposure (a slow cook off event). Either exposure can result in a high order detonation.
A non-functional (“safe”) mode is desirable so that firefighting efforts or demilitarizing procedures can be performed without the risk of a high order detonation from a single munition, or multiple munitions that may be packaged in a container such as in ammunition cans, pallets, and/or at an ammunition depot.
The design of munitions casings does not typically allow for the separation of the body after assembly. For example, the fragmentation body of a hand grenade is usually made of a cast iron member or a stamped metal with an embossed fragmentation pattern. The grenade body is made up of two pieces that are resistance welded, generally, along the diametric center of the body, thus creating a single piece body that functions as a pressure vessel for the energetics contained therein.
As a result of the detonation of the energetics, the munition is broken up and the fragments or the metal particles embedded in the body are scattered, causing damage to the surrounding environment. Such damage could be significant and in many cases unavoidable. For instance, if the munition were stored in a warehouse, a cook-off condition, whether slow or fast, would cause a chain reaction explosion or sympathetic detonation within the warehouse.
It is therefore an object of the present invention to provide a pressure discharge mechanism for closed vessels containing hazardous materials which automatically opens and/or vents said materials before the temperature and/or pressure in the vessel causes the vessel to rupture, and/or resulting in a high order detonation.
It is another object of the present invention to provide a pressure discharge mechanism that minimizes and/or eliminates high order detonations of closed vessels.
It is still another object of the present invention to provide a pressure discharge mechanism for closed vessels that provides a signal of an unsafe condition within the closed vessel to persons, such as, for example, fire fighters. It is yet another object of the present invention to provide a pressure discharge mechanism which will warn persons that the closed vessel has reached a critical condition, and that rupture and/or detonation thereof may be imminent. Prior to the advent of the present invention, the need for such a pressure discharge mechanism has heretofore remained unsatisfied.
It is yet another object of the present invention to provide a munition design that overcomes the afore mentioned problems associated with conventional munitions, and yet still functions normally under normal environmental conditions, with minimal manufacturing variances, in order to maintain the same user directions and training as for existing munitions, and to allow the use of conventional manufacturing procedures with minimal changes to the assembly lines. Prior to the advent of the present invention, the need for such a pressure discharge mechanism has heretofore remained unsatisfied.
For example, U.S. Pat. No. 6,752,085 provides an apparatus for releasably attaching a closure plate to an open end of a cylindrical casing, the apparatus having an inner member; a threaded outer ring biased in tension, disposed adjacent to the inner member, for releasably engaging an interior wall of the casing; and a eutectic spacer between the inner member and the outer ring. At temperatures below the melting point of the eutectic spacer, the outer ring is held in threaded engagement with the casing, and holds the closure plate in position in abutment with the casing. When the temperature of the eutectic spacer reaches its melting temperature, the eutectic spacer transitions to a liquid state, flows away from the apparatus, allowing the outer ring to retract into a groove in the inner member, and the closure to be released from the casing.
In another example, U.S. Pat. No. 5,398,498 provides a joint construction [that] is employed between a military rocket motor and a warhead adapted to be propelled be the motor. The motor includes a motor tube with a cylindrical front portion having an internal cylindrical surface therein. The warhead comprises an adapter ring having a cylindrical rear portion with an external cylindrical surface which is telescopically receivable within the internal cylindrical surface. The internal and external cylindrical surfaces are formed with respective confronting aligned internal and external helical screw thread grooves for receiving a fusible substantially helical joint member to form a secure connection between the rocket motor and the warhead. The helical joint member is made of a material having a low melting temperature, preferably a eutectic metal alloy, whereby the heat of a fire or the like will melt the joint member to disconnect the warhead from the rocket motor. The motor tube has a front wall with a vent operating therein, normally closed by a plug member. The adapter ring includes a means for retaining the plug member in the vent opening. The melting of the fusible joint member is effective to release the retaining action of the adapter ring, whereby any pressure in the motor tube expels the plug member and the adapter ring from the motor tube.